Novel interpolymer blends

ABSTRACT

Disclosed herein are polymer blends comprising a first interpolymer of a vinyl alcohol ester and at least one ethylenically unsaturated acid ester and a second interpolymer comprising a vinyl aromatic compound, at least one ethylenically unsaturated acid ester and at least one compound containing one or more acid groups. These blends are particularly useful as binders and adhesives.

United States Patent Blance et al. [4 Sept. 19, 1972 [541 NOVELINTERPOLYMER BLENDS [56] References Cited [72] Inventors: Robert B.Blance 26 Colony Dr.,

East Longmeadozv, Mass. 01028; U1 STATES PATENTS David R. C lm], 52 O klS 3,365,410 1/1968 Wesslau etal ..260/29.6 wilbmh M 01095; P t 2,934,5104/1960 Crissey et a]. ..260/3l.8 Nachtel, 1234 Wilbraham, Springfield,Mass. 01119 Primary Examiner--Murray Tillman [22] Filed: April 1971Assxstant Examiner-C. J. Seccuro [21] Appl. No.: 136,207 [57] ABSTRACTRelated A li fi Data Pisclosed herein are polymer blends comprising afirst mterpolymer of a vinyl alcohol ester and at least one [62]Dlvlslon of 783,700 1968 ethylenically unsaturated acid ester and asecond in- Q- terpolymer comprising a, vinyl aromatic compound, at leastone ethylenically unsaturated acid ester and at [52] U.S.Cl ..260/901,117/155 UA, 117/161 UT, least one compound containing one or more acid260/41 260/41 R, 260/335 UA groups. These blends are particularly usefulas binders [51] Int. Cl. ..C08f 41/12 and adhesives [5 8] Field ofSearch ..260/901 4 Claims, No Drawings NOVEL INTERPOLYMER BLENDSBACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to novel blends of interpolymers which are useful as binders andadhesives. More particularly, this invention relates to blends of afirst interpolymer comprising a vinyl alcohol ester and at least oneethylenically unsaturated acid ester and a second interpolymercomprising a vinyl aromatic compound, at least one ethylenicallyunsaturated acid ester and at least one ethylenically unsaturatedcompound containing at least one acid group.

2. Description of the Prior Art Electrophotography relates to substrateshaving a photoconductive substance coated thereon which provides asurface upon which images are reproducible. The substrate may, forexample, be paper, glass, metal foil, etc. The photoconductive substanceis a material having electrical conductivity dependent upon the amountof light to which it is subjected. The photoconductive layer, althoughnot light sensitive per se, is rendered so by applying to the coatedarticle an electrostatic charge (e.g., by Corona discharge). Images tobe reproduced are placed on top of the charged surface which is exposedto illumination by conventional photographic methods, whereby thecoating locally dissipates its charge inproportion to the intensity ofillumination. Non-illuminated areas, which retain their charge, are thentreated with electroscopic powder (e.g., colored synthetic resins)resulting in a visible image which may be transferred to another surfaceor may be fixed, e.g., by fusing, rendering the powder permanentlyadherent to the coating substrate.

Fundamentally, then, electrophotographic coatings comprise aphotoconductor such as, for example, zinc oxide, which is bonded by anorganic resin to a base sheet or other substrate. It is known thatcopolymers of vinyl acetate and copolymers of styrene are individuallyeffective as binders. Coatings based upon vinyl acetate copolymers,however, have been found to be deficient in speed. Further, coatings ofcopolymers of styrene have been found to be low in charge acceptance andyield copies of poor image density. Both deficiencies of the separatecopolymers may be overcome, at least in part, by blending the two typesof copolymers. The major drawback of such blends, however, has beentheir incompatibility as exhibited by their rapid phase separation. Suchseparation is a serious drawback to commercial utilization. It might beexpected that compatible blends useful in this area could be achieved bythe mere matching of solubility parameters. Attempts to achieve this,however, have been unsuccessful. It is necessary for commercial utilitythat the blended resins be compatible in solution concentrations of atleast 20 percent by weight. Imposed upon this requirement forcompatibility, however, is, of course, the requirement that the blendemployed ad here to the particular photoconductive element being used inthe system and to the substrate as well. In addition, the binderemployed must enhance the photoconductive properties of the system.

SUMMARY OF THE INVENTION This invention relates to a composition ofmatter comprising a first interpolymer of at least one vinyl alcoholester and at least one ethylenically unsaturated acid ester and a secondinterpolymer comprising at least one vinyl aromatic compound, at leastone ethylenically unsaturated acid and at least one ethylenicallyunsaturated compound containing at least one acid group.

More particularly, this invention relates to a composition of mattercomprising a blend of:

A. a first interpolymer comprising at least one vinyl alcohol ester andat least one ethylenically unsaturated acid ester containing at leastseven carbon atoms and B. a second interpolymer comprising 1. at leastone vinyl aromatic compound,

2. at least one ethylenically unsaturated acid ester,

and

3. 0.5 percent to 5.0 percent by weight, based upon the total weight ofthe second interpolymer, of at least one ethylenically unsaturatedcompound containing at least one acid group.

This invention also relates to the use of such blends in variousadhesive compositions wherein the term adhesive is construed asincluding binders.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The vinyl alcohol ester of thefirst interpolymer of the blends of this invention may be any vinylalcohol ester which is copolymerizable with the ethylenicallyunsaturated acid ester containing at least 7 carbon atoms. The choice ofthe particular vinyl alcohol to be employed will generally depend uponthe pigment which is to be included and the substrate to be coated. Thatis to say, the interpolymer produced should have the ability both to wetthe pigment and to adhere to the substrate. Examples of such vinylalcohol esters are vinyl formate, vinyl acetate, vinyl propionate, vinylbutyrate, vinyl pentanoate, vinyl hexanoate, vinyl heptanoate, vinyloctanoate, etc., their isomers and mixtures thereof. Where thecompositions of this invention are to be used as binders inelectrophotographic processes, it will usually be desirable that they beable to wet zinc oxide, a commonly used photoconductive pigment. Wherethis is the case it will generally be advantageous that a lower vinylalcohol ester e.g. vinyl formate, vinyl acetate, vinyl propionate, vinylbutyrate, or isomers thereof be employed. Thus, these four vinyl alcoholesters are the preferred vinyl alcohol esters in the practice of thisinvention. Vinyl acetate is most preferred because of its readycommercial availability and favorable capacity for interpolymerization.

A second component of the first interpolymer of the blends of thisinvention is an ethylenically unsaturated acid ester containing at leastseven carbon atoms. It is this component that is critical to theattainment of compatibility between the two interpolymers. Such estersmay of course be prepared by the reaction of organic acids and alcohols.The acid moiety of such esters may be monocarboxylic, polycarboxylic,monosulfonic, or polysulfonic acids such as, for example, acrylic acid,methacrylic acid, maleic acid, fumaric acid,

crotonic acid, vinyl sulfonic and the like. The alcohol moiety of theester may be any alcohol containing sufficient carbon atoms to bring thetotal number of carbon atoms of the ester moiety to at least 7. Thus thealcoholic moiety may, for example, be methanol, ethanol, propanol,butanol, pentanol, hexanol, heptanol, octanol, etc., their isomers andmixtures thereof. Of those compounds which may be used as the secondcomponent of the first interpolymer, acrylic and methacrylic acid estersare preferred. In particular, it has been found that butyl acrylateprovides optimal properties for electrophotographic coatings wheninterpolymerized with vinyl acetate and is thus the most preferredester.

In addition to the two critical components of the first interpolymerdescribed above, other monomers may be interpolymerized therewith toimpart particular desirable qualities to the resin. In particular, ithas been found beneficial and desirable in photoconductiveelectrophotographic applications that an ethylenically unsaturated acidester containing four to six carbon atoms be included, for example,methyl acrylate, ethyl acrylate, propyl acrylate, methyl methacrylate,ethyl methacrylate, and the like. Other esters such as dimethyl maleate,dimethyl fumarate and the like may be employed.

The vinyl aromatic compound moiety of the second interpolymer ispreferably styrene. However, ring-substituted styrenes in which thesubstituents are one to four carbon atoms alkyl groups or chlorine atomsmay be employed. Examples of such ring-substituted styrenes includeortho-, metaand paramethyl, ethyl, butyl, etc., mono-alkyl styrenes,2,3-2,4-dimethyl and diethyl styrenes; mono-, diand trichlorostyrenes;alkyl chlorostyrenes such as 2-methyl-4-chlorostyrene, etc. The use oftwo or more such styrene monomer moieties is also within the scope ofthis invention. The ethylenically unsaturated acid ester whichconstitutes a second component of the second interpolymer may be anyalkyl ester of an ethylenically unsaturated monocarboxylic orpolycarboxylic acid, e.g., methyl acrylate, methyl methacrylate, methylcrotonate, ethyl acrylate, ethyl methacrylate, ethyl crotonate, dimethylmaleate, dimethyl fumarate, diethyl maleate, dipropyl itaconate, butylcrotonate, and the like. The preferred ester is ethyl acrylate.

The second interpolymer further contains at least one ethylenicallyunsaturated compound containing at least one acid group. This acid groupmay be a carboxylic acid group or a sulfonic acid group. Examples ofcompounds which may be employed are acrylic acid, methacrylic acid,crotonic acid, maleic acid, fumaric acid; mono esters and partial monoesters of maleic acid, fumaric acid, itaconic acid, e.g., mono methylmaleate, monoethyl fumarate, etc.; vinyl sulfonic acid, styrene sulfonicacid, sulfoethyl methacrylate, sulfoethyl acrylate, sulfoethyl maleate,and the like.

Any of various pigments may be dispersed in the compositions of thisinvention so long as it has adhesive affinity for the particularcomposition employed. By adhesive affinity is meant that the compositionwill adhere to the pigment and act as a binder therefor. Exemplary ofthe many pigments which might be used are titanium dioxide, ferricoxide, graphite, lead oxide, lead chromate and the like. Where thecompositions of this invention are to be used as binders inelectrophotographic processes the pigment will be one capable of beingrendered light sensitive by the application thereto of an electrostaticcharge. As examples of such photoconductors may be listed antimonyoxide, aluminum oxide, bismuth oxide, cadmium oxide, mercury oxide,molybdenum oxide, lead oxide, zinc iodide, cadmium iodide, cadmiumsulfide, selenium metal, arsenic trisulfide, lead telluride and thelike. In particular, zinc oxide is preferred for such application.Mixtures of two or more pigments may also be employed.

For such electrophotographic processes, various organic photoconductorsmay also be used either in addition to the inorganic, e.g. zinc oxide,or in place of them. Aromatic amines may, for example, be employed forthis purpose. Among the many that may be used are4,5-Diphenyl-2-imidazolone, 4,5-diphenylimidazole-2- thione and theirderivatives, l-phenyl-3,5-bis(pmethoxy-styryl)pyrazoline, polymers ofN-vinyl carbozole, 4,4"-clibromoterphenyl, poly( 9-vinyl anthracene),etc.

The following examples are presented in illustration of the inventionbut are not to be construed as limitations thereof. Where parts arementioned, parts by weight are intended unless otherwise indicated.

EXAMPLE 1 PART A Into a reaction vessel equipped with an agitator, acondenser, a thermometer and a metering pump for controlled, delayedmonomer input is introduced 500 parts of vinyl acetate, 14 parts ofethyl acrylate, 14 parts of butyl acrylate, parts toluene, 5 parts ofbenzoyl peroxide and 2 parts of t-butyl perbenzoate. The mixture is thenheated to reflux. In a separate container is mixed 236 parts of ethylacrylate, 236 parts of butyl acrylate and 200 parts of toluene. Thismixture is then introduced into the reservoir supplying the meteringpump and addition of the delay and monomer charge is begun. The delay iscarried out over 4 40 minute periods. During the first 40 minute period306 parts of the delayed monomer mixture is added, during the second 40minute period 210 parts, during the third 40 minute period 107 partsand, finally, during the last 40 minute period the final 50 parts ofdelay is added. The batch is then held at reflux for an additional 4hours. The solution is diluted with 230 parts of toluene and then cooledto room temperature. The resulting polymer containing solution has atotal solids content of 67 percent and a Brookfield viscosity (No. 4spindle at 12 r.p.m.) of 36,000.

PART B Into a reaction vessel equipped as in Part A above is introducedparts of styrene, 250 parts of ethyl acrylate, 200 parts of toluene, 1.0part of acrylic acid and 4 parts of t-butyl perbenzoate. The batch isheated to reflux. A delay charge consisting of 75 parts of styrene,parts of toluene and 4.0 parts acrylic acid is mixed in a separatevessel. The delay is added over a 4 hour period. During the first hour136 parts of delay is added, during-the second hour 67 parts, during thethird hour 34 parts and, finally, during the fourth hour 17 parts. Thebatch is held at reflux for an additional 16 hours and then cooled toroom temperature yielding a polymer solution having a total solids of58.2 percent and a Brookfield viscosity (No. 4 spindle at 40 rpm.) of7,100.

PART C I Parts of the 67 percent solids solution of Part A is mixed with23 parts of the 58 percent solids solution of Part B and 5.7 parts oftoluene is added thereto to yield a 55 percent solids solution of theblends. Visual examination shows that this solution blend is compatible.

PART D 68'Parts of the 55 percent solution prepared in Part C is weighedinto a Waring Blender. 144 Parts of toluene is added and the new mixtureis well agitated. Next is added 225 parts of a French process zinc oxideand agitation is continued at high speed for 7-l0 minutes. 4.5 Parts ofa k percent solution in methanol of a sensitizing dye is then added withthorough mixing. The dispersion thus prepared is applied to acommercially available conductive base-stockpaper to a coating weight of20 lbs. per ream. The coated paper is then dried and conditioned at 50percent relative humidity in the dark and then tested for chargeacceptance, dark decay charge and decay of charge during illuminationusing a Victoreen Model EPA-825 electrostatic paper analyzer. Theprocedure by which this is accomplished is set forth in RCA Review,Dec., 1961, Pages 780-790. For the coating prepared in this example acharge acceptance is 440 volts, the dark decay of charge is 7.5 voltsper second and the decay of charge during illumination is 104 volts persecond.

EXAMPLE 2 CONTROL Example 1 is repeated using the interpolymer of Example l Part A and substituting for the interpolymer of Example 1, PartB an interpolymer containing no acrylic acid, i.e., 50/50 styrene/ethylacrylate rather than 49/50/1 styrene/ethyl acrylate/acrylic acid. Theblended resin solutions are incompatible and no coating is obtainableupon which to test the electric properties.

EXAMPLE 3 Example 1 is repeated substituting for the interpolymer ofPart B an interpolymer of 49.5/50/0.5 styrene/ethyl acrylate/acrylicacid. Again, the blend is found to be compatible to toluene and theelectrical properties are: charge acceptance, 425 volts; dark decay ofcharge, 10 volts per second; and decay of charge during illumination, 94volts per second.

EXAMPLE 4 Example 1 is repeated substituting for the interpolymer ofPart B an interpolymer of 45/50/50 styrene/ethyl acrylate/acrylic acid.This blend is compatible in a solution with toluene and n-propanol andthe electrical properties are 515 volts charge acceptance, 5.0 volts persecond dark decay and 135 volts per second illuminated decay.

EXAMPLE 5 Example 1 is repeated except that a '60/40 vinyl acetate/butylacrylate copolymer is substituted for the 50/25/25 vinyl acetate/ethylacrylate/butyl acrylate interpolymer employed therein. The blend isfound to be compatible in toluene solution and the electrical propertiesare 441 volts charge acceptance, 7.0 volts per second dark decay and 86volts per second illuminated decay.

EXAMPLE 6 CONTROL Example 1 is repeated except that a copolymer of /30vinyl acetate/methyl acrylate is substituted for the interpolymer ofPart A. This time the blend is incompatible in toluene solution and thecharge acceptance is only 166 volts. Dark decay is 5.0 volts-per secondand illuminated decay is 94 volts per second.

This example demonstrates the deficiencies of a system not containing anethylenically unsaturated acid ester containing at least seven carbonatoms as a part of the first interpolymer.

EXAMPLE 7 Into a reaction vessel is charged parts styrene, 250 parts ofethyl acrylate and 1 part of 2-sulfoethyl methacrylate, 370 parts oftoluene and 8 parts of tbutyl perbenzoate. An additional 65 parts ofstyrene and 4 parts of sulfoethyl methacrylate blended with 5 parts oftoluene are added to the reaction in two separate streams over a 4 hourperiod while the batch is held at reflux. The reaction is maintained atreflux for an additional 20 hours and is cooled yielding a polymericsolution of 67.5 percent solids. The Brookfield viscosity is 1,600centipoises (No. 3 spindle at 30 rpm). The resulting interpolymer isthen substituted for the interpolymer of Example 1, Part B and the finalproduct is found to have a charge acceptance of 448 volts, a dark decayof 4.0 volts per second and an illuminated decay of 107 volts persecond.

EXAMPLE 8 Example 1 is repeated except that an interpolymer of 47/50/3chlorostyrene/ethyl acrylate/acrylic acid is substituted for theinterpolymer of Part B. The blend is again found to be compatible intoluene and the electrical properties are 177 volts charge acceptance,4.5 volts per second dark decay and 87 volts per second illuminateddecay.

It will be noted that in the foregoing examples the first and secondinterpolymers have been blended in 1:1 ratios. It is not necessary tothe practice of this invention that such be the case. The 1:1 ratio waschosen as being the most rigorous test of compatibility; that is to say,if compatibility can be shown at 1:1, it will also be achievable whereone or the other of the components is present in major proportions. Forparticular applications as, for example, in electrophotographyoptimization of a particular system well may dictate variations inproportion as divergent as 9:1 or 1:9 or even beyond.

Further, it should be noted that although the examples show onlyapplication to paper substrates, they may also be successfully appliedto metal, glass, ceramics and, in particular, wooden substrates. Thus,upon formulation with the various pigments, fillers, driers, extenders,dyes, etc., well known to those of skill in the art, paints and othercoatings for application to a wide variety of surfaces may be produced.

Thus, it will be obvious that many variations and modifications may beapplied to the invention described herein without departing from thescope thereof.

What is claimed is:

1. A composition of matter comprising a blend of:

A. a first interpolymer consisting of an interpolymerization produce ofat least one vinyl alcohol ester and at least one ester of acrylic acidcontaining at least seven carbon atoms and B. a second interpolymerconsisting of an interpolymerization product of:

l. at least one vinyl aromatic compound, 2. at least one ester ofacrylic acid and 3. 0.5 to 5.0 percent by weight, based upon the totalweight of the second interpolymer of at least one ethylenicallyunsaturated compound containing at least one acid group;

wherein the weight ratio of the first interpolymer to the secondinterpolymer is in the range from 9:1 to 1:9.

2. The composition of claim 1 wherein the first interpolymer comprisesan interpolymerization product of:

A. at least one vinyl alcohol ester, B. at least one ester of acrylicacid containing at least seven carbon atoms and C. at least one ester ofacrylic acid containing four to six carbon atoms. 3. The composition ofclaim 1 dissolved in a compatible organic solvent.

4. The composition of claim 3 having dispersed therein at least onepigment having adhesive affinity for the interpolymer blend thereof.

2. at least one ester of acrylic acid and
 2. The composition of claim 1wherein the first interpolymer comprises an interpolymerization productof: A. at least one vinyl alcohol ester, B. at least one ester ofacrylic acid containing at least seven carbon atoms and C. at least oneester of acrylic acid containing four to six carbon atoms.
 3. Thecomposition of claim 1 dissolved in a compatible organic solvent.
 3. 0.5to 5.0 percent by weight, based upon the total weight of the secondinterpolymer of at least one ethylenically unsaturated compoundcontaining at least one acid group; wherein the weight ratio of thefirst interpolymer to the second interpolymer is in the range from 9:1to 1:9.
 4. The composition of claim 3 having dispersed therein at leastone pigment having adhesive affinity for the interpolymer blend thereof.